Pioneer 11

Pioneer 11, also known as Pioneer G, was a robotic space probe launched by NASA on April 5, 1973. Its mission was to study the asteroid belt, explore the environments around Jupiter and Saturn, and examine the solar wind and cosmic rays. It was the first probe to visit Saturn and the second to travel through the asteroid belt and fly by Jupiter.

As it continued its journey, Pioneer 11 became the second of five human-made objects to leave our Solar System entirely, reaching an escape velocity. Because of the huge distances involved and limited power, scientists lost regular contact with the spacecraft on September 30, 1995, and the last clear engineering data came in on November 24, 1995. Today, Pioneer 11 remains a remarkable achievement in space exploration.

Mission background

History

In February 1969, NASA approved Pioneer 11 and its twin probe, Pioneer 10, to explore the outer Solar System. These were the first probes designed for this purpose. Early goals included studying the space between planets beyond Mars, checking the asteroid belt for dangers to future missions, and exploring the environment of Jupiter. Later, they added many goals for when the probe would reach Saturn, like mapping Saturn’s magnetic field, studying its atmosphere, and measuring temperatures.

Spacecraft design

Pioneer 11 was built to travel far from Earth. It was about 36 centimeters deep and had a hexagonal shape made of six panels. The spacecraft weighed 259 kilograms and carried tools to study space. It used special fuel called hydrazine to stay pointed in the right direction and had sensors to know where Earth and the Sun were.

The probe could send messages back to Earth using antennas and powerful transmitters. It was powered by four special generators that turned heat from radioactive material into electricity. Pioneer 11 also carried computers to store and send back information from its science tools, including one extra instrument that measured magnetic fields.

Helium Vector Magnetometer (HVM)
	Measures the fine structure of the interplanetary magnetic field, mapped the Jovian magnetic field, and provides magnetic field measurements to evaluate solar wind interaction with Jupiter. Principal investigator: Edward Smith / JPL Data: PDS/PPI data catalog, Quadrispherical Plasma Analyzer
	Peer through a hole in the large dish-shaped antenna to detect particles of the solar wind originating from the Sun. Principal investigator: Aaron Barnes / NASA Ames Research Center (PDS/PPI data catalog, Charged Particle Instrument (CPI)
	Detects cosmic rays in the Solar System. Principal investigator: John Simpson / University of Chicago Data: Cosmic Ray Telescope (CRT)
	Collects data on the composition of the cosmic ray particles and their energy ranges. Principal investigator: Frank B. McDonald / NASA Goddard Space Flight Center Data: PDS/PPI data catalog, Geiger Tube Telescope (GTT)
	Surveys the intensities, energy spectra, and angular distributions of electrons and protons along the spacecraft's path through the radiation belts of Jupiter and Saturn. Principal investigator: James A. Van Allen / University of Iowa (website) Data: PDS/PPI data catalog, NSSDC Jupiter data archive
Trapped Radiation Detector (TRD)
	Includes an unfocused Cerenkov counter that detects the light emitted in a particular direction as particles passed through it recording electrons of energy, 0.5 to 12 MeV, an electron scatter detector for electrons of energy, 100 to 400 keV, and a minimum ionizing detector consisting of a solid-state diode that measured minimum ionizing particles ( Principal investigator: R. Fillius / University of California San Diego Data: NSSDC Saturn data archive
Meteoroid Detectors
	Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids. Principal investigator: William Kinard / NASA Langley Research Center Data: NSSDC data archive list
Asteroid/Meteoroid Detector (AMD)
	Meteoroid-asteroid detector looks into space with four non-imaging telescopes to track particles ranging from close by bits of dust to distant large asteroids. Principal investigator: Robert Soberman / General Electric Company Data: NSSDC data archive list
Ultraviolet Photometer
	Ultraviolet light (200 to 800 Å) is sensed to determine the quantities of hydrogen and helium in space and on Jupiter and Saturn. Principal investigator: Darrell Judge / University of Southern California Data: PDS/PPI data catalog, Imaging Photopolarimeter (IPP)
	The imaging experiment relies upon the spin of the spacecraft to sweep a small telescope across the planet in narrow strips only 0.03 degrees wide, looking at the planet in red (5800 to 7000 Å) and blue (3900 to 4900 Å) light. These strips are then processed to build up a visual image of the planet. Principal investigator: Tom Gehrels / University of Arizona Data: NSSDC data archive list
Infrared Radiometer
	Provides information on cloud temperature and the output of heat from Jupiter and Saturn. Principal investigator: Andrew Ingersoll / California Institute of Technology
Triaxial Fluxgate Magnetometer
	Measures the magnetic fields of both Jupiter and Saturn. This instrument is not carried on Pioneer 10. Principal investigator: Mario Acuna / NASA Goddard Space Flight Center Data: NSSDC data archive list

Mission profile

Launch and trajectory

The Pioneer 11 probe was launched on April 6, 1973, by the National Aeronautics and Space Administration from Cape Canaveral, Florida. It was sent to study the asteroid belt, Jupiter, Saturn, the solar wind, and cosmic rays. It was the first probe to visit Saturn and the second to visit Jupiter and the asteroid belt.

Encounter with Jupiter

Main article: Exploration of Jupiter

Pioneer 11 flew past Jupiter in late 1974. It came very close to the planet, passing about 42,828 kilometers above the clouds. It sent back the first images of Jupiter's polar regions and helped scientists learn more about Jupiter's moon Callisto.

Encounter with Saturn

Main article: Exploration of Saturn

Pioneer 11 passed by Saturn on September 1, 1979. It came within 21,000 kilometers of Saturn. It also came close to one of Saturn's small moons and sent back pictures of Saturn's rings.

Interstellar mission

On February 25, 1990, Pioneer 11 became the fourth human-made object to travel beyond the orbit of the planets. By 1995, it could no longer power its instruments, so NASA stopped regular contact with the spacecraft.

Timeline

Current status

The last time we talked to Pioneer 11 was on September 30, 1995. Since then, it has traveled very far away from Earth. As of June 24, 2024, Pioneer 11 is about 113 AU from Earth and 114 AU from the Sun. It moves at a speed of 11.155 km/s and heads toward the constellation Scutum.

Later, Pioneer 11 was passed by the Voyager probes launched in 1977. Voyager 1 is now the farthest human-made object in space.

Pioneer anomaly

Main article: Pioneer anomaly

Scientists noticed something strange in the signals from the Pioneer 10 and 11 space probes when they were far from the Sun. The signals seemed to change in a way that suggested the probes were being pulled slightly toward the Sun. For a long time, they weren’t sure why this was happening. Later, they found out that the heat given off by parts of the probes was pushing them a tiny bit, creating this effect known as the "Pioneer anomaly."

Pioneer plaque

Main article: Pioneer plaque

The Pioneer 10 and Pioneer 11 spacecraft each carried a special plaque made of gold-coated aluminum. This was in case the spacecraft were ever found by intelligent life from other planets. The plaques showed a man and a woman without clothes, along with symbols to tell where the spacecraft came from.

Commemoration

In 1991, Pioneer 11 was featured on a stamp made by the United States Postage Service. The stamp celebrated spacecraft that explored the planets and the Moon. Pioneer 11 was shown with Jupiter, while Pluto was noted as "Not yet explored."